I'm writing a RS485 driver for an ARM AT91SAM9260 board on Linux.
When I initialise the UART, the RTS signal line gets high (1). I guess this would and should be the standard behaviour in RS232 operation mode. In RS485 mode however this is not wanted.
I'm using the standard functions provided by the arm-arch section to initialise the UART. Therefore the significant steps are:
at91_register_uart(AT91SAM9260_ID_US2, 3, ATMEL_UART_CTS | ATMEL_UART_RTS);
//consisting of:
// >> configure/mux the pins
at91_set_A_periph(AT91_PIN_PB10, 1); /* TXD */
at91_set_A_periph(AT91_PIN_PB11, 0); /* RXD */
if (pins & ATMEL_UART_RTS)
at91_set_B_periph(AT91_PIN_PC8, 0); /* RTS */
if (pins & ATMEL_UART_CTS)
at91_set_B_periph(AT91_PIN_PC10, 0); /* CTS */
// >> associate the clock
axm_clock_associate("usart3_clk", &pdev->dev, "usart");
// >> et voilĂ
As you can see with
at91_set_B_periph(AT91_PIN_PC8, 0);
the pull-up on the RTS pin isn't activated.
Why does the UART set the RTS high? Just because this would be the standard behaviour in RS232 mode?
Wouldn't it be a better standard for the UART to keep silent till the
operation mode is explicitly set?